In gas turbine engines, there is a preferred ratio between the diameters of the high-pressure turbine spool and the low-pressure turbine spool. Specifically, the low-pressure turbine spool has a larger diameter than the high-pressure turbine spool to provide optimal engine performance. Because of this difference in radial size, the transition duct joining the high-pressure and low-pressure turbines must accommodate this change in radius.
However, increasing the size of the duct over a relatively short distance can result in boundary layer separation of the flow within the duct, adversely affecting low-pressure turbine performance. Therefore, gas turbine engines are often designed with elongated transition ducts, or transition ducts that do not achieve the optimal ratio between the high-pressure turbine size and the low-pressure turbine size.
Therefore, there is a need for continued improvement in the design of such inter-turbine transition ducts.